Move function HTTPHandler::formatExceptionForClient() to a separate header in order to reuse it.

src/Server/HTTP/sendExceptionToHTTPClient.cpp

@@ -0,0 +1,80 @@
+#include <Server/HTTP/sendExceptionToHTTPClient.h>
+
+#include <Server/HTTP/HTTPServerRequest.h>
+#include <Server/HTTP/WriteBufferFromHTTPServerResponse.h>
+#include <Server/HTTP/exceptionCodeToHTTPStatus.h>
+
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int HTTP_LENGTH_REQUIRED;
+    extern const int REQUIRED_PASSWORD;
+}
+
+
+void sendExceptionToHTTPClient(
+    const String & exception_message,
+    int exception_code,
+    HTTPServerRequest & request,
+    HTTPServerResponse & response,
+    WriteBufferFromHTTPServerResponse * out,
+    LoggerPtr log)
+{
+    setHTTPResponseStatusAndHeadersForException(exception_code, request, response, out, log);
+
+    if (!out)
+    {
+        /// If nothing was sent yet.
+        WriteBufferFromHTTPServerResponse out_for_message{response, request.getMethod() == HTTPRequest::HTTP_HEAD, DEFAULT_HTTP_KEEP_ALIVE_TIMEOUT};
+
+        out_for_message.writeln(exception_message);
+        out_for_message.finalize();
+    }
+    else
+    {
+        /// If buffer has data, and that data wasn't sent yet, then no need to send that data
+        bool data_sent = (out->count() != out->offset());
+
+        if (!data_sent)
+            out->position() = out->buffer().begin();
+
+        out->writeln(exception_message);
+        out->finalize();
+    }
+}
+
+
+void setHTTPResponseStatusAndHeadersForException(
+    int exception_code, HTTPServerRequest & request, HTTPServerResponse & response, WriteBufferFromHTTPServerResponse * out, LoggerPtr log)
+{
+    if (out)
+        out->setExceptionCode(exception_code);
+    else
+        response.set("X-ClickHouse-Exception-Code", toString<int>(exception_code));
+
+    /// If HTTP method is POST and Keep-Alive is turned on, we should try to read the whole request body
+    /// to avoid reading part of the current request body in the next request.
+    if (request.getMethod() == Poco::Net::HTTPRequest::HTTP_POST && response.getKeepAlive()
+        && exception_code != ErrorCodes::HTTP_LENGTH_REQUIRED)
+    {
+        try
+        {
+            if (!request.getStream().eof())
+                request.getStream().ignoreAll();
+        }
+        catch (...)
+        {
+            tryLogCurrentException(log, "Cannot read remaining request body during exception handling");
+            response.setKeepAlive(false);
+        }
+    }
+
+    if (exception_code == ErrorCodes::REQUIRED_PASSWORD)
+        response.requireAuthentication("ClickHouse server HTTP API");
+    else
+        response.setStatusAndReason(exceptionCodeToHTTPStatus(exception_code));
+}
+}

src/Server/HTTP/sendExceptionToHTTPClient.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <Common/logger_useful.h>
+#include <base/types.h>
+
+
+namespace DB
+{
+class HTTPServerRequest;
+class HTTPServerResponse;
+class WriteBufferFromHTTPServerResponse;
+
+/// Sends an exception to HTTP client. This function doesn't handle its own exceptions so it needs to be wrapped in try-catch.
+/// Argument `out` may be either created from `response` or be nullptr (if it wasn't created before the exception).
+void sendExceptionToHTTPClient(
+    const String & exception_message,
+    int exception_code,
+    HTTPServerRequest & request,
+    HTTPServerResponse & response,
+    WriteBufferFromHTTPServerResponse * out,
+    LoggerPtr log);
+
+/// Sets "X-ClickHouse-Exception-Code" header and the correspondent HTTP status in the response for an exception.
+/// This is a part of what sendExceptionToHTTPClient() does.
+void setHTTPResponseStatusAndHeadersForException(
+    int exception_code, HTTPServerRequest & request, HTTPServerResponse & response, WriteBufferFromHTTPServerResponse * out, LoggerPtr log);
+}

src/Server/HTTPHandler.cpp

@@ -33,7 +33,7 @@
 #include <base/scope_guard.h>
 #include <Server/HTTP/HTTPResponse.h>
 #include <Server/HTTP/authenticateUserByHTTP.h>
-#include <Server/HTTP/exceptionCodeToHTTPStatus.h>
+#include <Server/HTTP/sendExceptionToHTTPClient.h>
 #include <Server/HTTP/setReadOnlyIfHTTPMethodIdempotent.h>
 #include <boost/container/flat_set.hpp>
 
@@ -60,8 +60,6 @@ namespace ErrorCodes
 
     extern const int NO_ELEMENTS_IN_CONFIG;
 
-    extern const int REQUIRED_PASSWORD;
-
     extern const int INVALID_SESSION_TIMEOUT;
     extern const int HTTP_LENGTH_REQUIRED;
 }
@@ -519,7 +517,7 @@ void HTTPHandler::processQuery(
             {
                 bool with_stacktrace = (params.getParsed<bool>("stacktrace", false) && server.config().getBool("enable_http_stacktrace", true));
                 ExecutionStatus status = ExecutionStatus::fromCurrentException("", with_stacktrace);
-                formatExceptionForClient(status.code, request, response, used_output);
+                setHTTPResponseStatusAndHeadersForException(status.code, request, response, used_output.out_holder.get(), log);
                 current_output_format.setException(status.message);
                 current_output_format.finalize();
                 used_output.exception_is_written = true;
@@ -553,7 +551,7 @@ void HTTPHandler::trySendExceptionToClient(
     const std::string & s, int exception_code, HTTPServerRequest & request, HTTPServerResponse & response, Output & used_output)
 try
 {
-    formatExceptionForClient(exception_code, request, response, used_output);
+    setHTTPResponseStatusAndHeadersForException(exception_code, request, response, used_output.out_holder.get(), log);
 
     if (!used_output.out_holder && !used_output.exception_is_written)
     {
@@ -615,38 +613,6 @@ catch (...)
     used_output.cancel();
 }
 
-void HTTPHandler::formatExceptionForClient(int exception_code, HTTPServerRequest & request, HTTPServerResponse & response, Output & used_output)
-{
-    if (used_output.out_holder)
-        used_output.out_holder->setExceptionCode(exception_code);
-    else
-        response.set("X-ClickHouse-Exception-Code", toString<int>(exception_code));
-
-    /// FIXME: make sure that no one else is reading from the same stream at the moment.
-
-    /// If HTTP method is POST and Keep-Alive is turned on, we should try to read the whole request body
-    /// to avoid reading part of the current request body in the next request.
-    if (request.getMethod() == Poco::Net::HTTPRequest::HTTP_POST && response.getKeepAlive()
-        && exception_code != ErrorCodes::HTTP_LENGTH_REQUIRED)
-    {
-        try
-        {
-            if (!request.getStream().eof())
-                request.getStream().ignoreAll();
-        }
-        catch (...)
-        {
-            tryLogCurrentException(log, "Cannot read remaining request body during exception handling");
-            response.setKeepAlive(false);
-        }
-    }
-
-    if (exception_code == ErrorCodes::REQUIRED_PASSWORD)
-        response.requireAuthentication("ClickHouse server HTTP API");
-    else
-        response.setStatusAndReason(exceptionCodeToHTTPStatus(exception_code));
-}
-
 void HTTPHandler::handleRequest(HTTPServerRequest & request, HTTPServerResponse & response, const ProfileEvents::Event & write_event)
 {
     setThreadName("HTTPHandler");

src/Server/HTTPHandler.h

@@ -173,12 +173,6 @@ private:
         HTTPServerResponse & response,
         Output & used_output);
 
-    void formatExceptionForClient(
-        int exception_code,
-        HTTPServerRequest & request,
-        HTTPServerResponse & response,
-        Output & used_output);
-
     static void pushDelayedResults(Output & used_output);
 };